In recent years the use of sodium perborate as bleaching agent in bleaching detergent compositions has become widespread. It has a number of advantages, especially in combination with bleach activators such as tetra acetyl ethylene diamine (TAED), which enables effective bleaching at lower temperatures down to 40.degree. C. The function of the perborate in this bleach system is to provide a stable source of hydrogen peroxide. A number of other inorganic peroxides which are capable of liberating hydrogen peroxide have also been considered. An example of such a compound is sodium percarbonate, having the formula 2Na.sub.2 CO.sub.3.3H.sub.2 O.sub.2
Unfortunately, when conventional sodium percarbonate is admixed to a detergent base powder, it is rapidly decomposed at temperatures of above 30.degree. C. and under humid atmospheric conditions. Thus the use of the sodium percarbonate as a bleaching agent in detergent powders has up to now been severely restricted by its limited storage stability.
Various attempts have been made to improve the stability of sodium percarbonate in detergent formulations. For instance, it has been proposed in GB-A-2 019 825 (Kao) to coat the percarbonate particles by spraying a solution containing an alkaline earth metal salt onto the particles.
GB-A-1 451 719 (Kao) discloses that the stability of a percarbonate containing phosphate built detergent composition can be improved when at least 60% by weight of the base powder and of the percarbonate has a particle diameter larger than 250 .mu.m, provided that the copper content of the base powder is less than 2 ppm and the iron content is less than 5 ppm.
The storage stability of sodium percarbonate in zeolite built detergent powders constitutes an even greater problem, possibly because of their large mobile water contents.
GB-A-2 013 259 discloses that the stability of sodium percarbonate in a zeolite built formulation may be improved if special requirements are met with regard to the zeolite, which must be either less than 75% crystalline or else may be of any crystallinity and have 1 to 10% of its sodium ions replaced by calcium and/or magnesium.
We have now found that the stability of a zeolite built detergent powder which contains sodium percarbonate as bleaching agent may be substantially improved by controlling the morphology of the percarbonate.